(1) Field of the Invention
The present invention relates to a composition for artificial marble having a deep appearance characteristic of marble and having a high strength and high abrasion resistance.
(2) Description of the Related Art
Artificial marble has been heretofore used as sanitary wares such as a washing stand, a bathtub and a kitchen counter, or as construction materials such an interior decorative material and an exterior decorative material.
For the production of artificial marble in the form of a resin molded article, there is adopted a cast molding method comprising incorporating, for example, an inorganic filler or a fibrous filler into a matrix resin constituting artificial marble, kneading the mixture, and filling and curing the kneaded composition in a mold. There also is adopted a molding method in which SMC (sheet molding compound) formed by impregnating a glass fiber or the like with a resin composition having an inorganic filler or other bulking agent incorporated therein and wrapping both the surfaces with a film or BMC (bulk molding compound) similarly prepared in the form of a bulk is compression-molded.
An unsaturated polyester resin and an epoxy resin are generally used as the matrix resin, but artificial marbles prepared by using these matrix resins not entirely satisfactory in appearance. For example, artificial marble prepared by using an unsaturated polyester resin as the matrix is defective in that since the transparency is insufficient, a deep appearance based on the transparency, which is characteristic of marble, cannot be obtained. A technique of overcoming this defect is proposed, for example, in Japanese Unexamined Patent Publication No. 59-66426 or Japanese Unexamined Patent Publication No. 61-101552.
Moreover, a product obtained by using an unsaturated polyester resin as the matrix is defective in that, since the scratch resistance of the surface is insufficient, a gel coating agent must be used.
The trend in the uses of artificial marble toward an increase of the quality is strong at the present, and the attainment of a pleasing appearance having a pattern deep in the interior of the molded article, which is due to a high transparency, and an improvement of the mechanical properties such as flexural strength and impact resistance, surface strength and mechanical strength, are desired. Therefore, a methacrylic resin having a good transparency and mechanical strength has attracted attention as the matrix resin, and many proposals have been made for an artificial marble composition or artificial marble comprising a methacrylic resin as the matrix, and many inventions characterized by the combined use of a methacrylic resin with a specific filler have been published. For example, there can be mentioned a method in which aluminum hydroxide is added (see Japanese Examined Patent Publication No. 50-22586 and Japanese Examined Patent Publication No. 55-43422), a method in which silica is added (Japanese Unexamined Patent Publication No. 58-4611), and a method in which calcium silicate is added (Japanese Unexamined Patent Publication No. 59-33308).
Furthermore, there is disclosed a composition of a methacrylic acid type resin having a filler incorporated therein, in which the flowability at the molding step is improved (Japanese Unexamined Patent Publication No. 60-245609).
As seen from the foregoing description, a methacrylic resin is now used as the matrix resin more frequently than the heretofore used unsaturated polyester resin or epoxy resin.
Also, as pointed out above, if a resin having an excellent transparency is used as the matrix for artificial marble, a deep and pleasing appearance can be given to the molded artificial marble. Therefore, it is generally considered that a methacrylic resin is preferably used as the matrix resin. The methacrylic resin however, is far different from a filler in various properties, and especially, because of differences of interfacial characteristics, the methacrylic resin has a poor affinity and adhesiveness to the filler. Moreover, when the filler is incorporated into the resin, the viscosity increases with the incorporation of the filler, and it becomes extremely difficult to disperse the filler uniformly in the resin. Accordingly, it is difficult to improve the characteristics of artificial marble and reduce the cost by increasing the amount of the filler.
For the foregoing reason, the obtained artificial marbles involves a problem in that the mechanical strength characteristics such as the flexural strength and impact resistance are not practically satisfactory. To overcome this defect, artificial marble formed by incorporating into a resin a filler having the surface treated with a silane coupling agent is proposed, but a satisfactory improvement cannot be attained by this proposal. Moreover, an increase of the manufacturing cost cannot be avoided.
Moreover, the methacrylic resin is fatally defective in that the resistance to boiling water is low and the artificial marble composition cannot be used for a bathtub and the like.